This invention relates to a radial type hydraulic pump motor comprising a rotating cylinder block and a drum case rotating eccentrically with said cylinder block.
An object of the present invention is to provide a radial type hydraulic pump motor wherein a piston couplingly inserted into a cylinder block is formed at the head portion thereof with a concave or convex spherical surface, with which is engaged a piston shoe having a convex or concave surface at the inner side thereof and a planar surface at the outer side thereof, further a crescent-shaped segment having a curvature equal to the inner surface of the drum case at the outer side and a planar surface at the inner side thereof is interposed between said piston shoe and the inner peripheral surface of drum case, and a pressure balancing recess communicated with a cylinder chamber through a small diameter passageway is provided in the outer planar portion of piston shoe, whereby said pump motor is suitable for operation under high pressure and can attain a high efficiency and long service life.
Additionally, another object of the present invention is to provide a radial type hydraulic pump motor wherein the segment is provided at opposite end portions thereof with guide projections, retaining plates are floatingly provided at both sides of the cylinder block, said plate have guide grooves for coupling to said guide projections and are adapted to regulate the segment in both radial and circumferential directions of drum case, said retaining plate is provided with a plurality of guide holes for bringing the rotating movements of segment and cylinder block in synchronism, and said guide holes are adapted to be guided by rollers which are mounted at opposite ends of a plurality of pins inserted into and secured to the cylinder block, the diameter of said guide hole is made equal to the sum of the diameter of roller and doubled value of eccentricity to permit the retaining plate to rotate coaxially with the drum case while the cylinder block is rotating eccentrically whereby the segment is controlled in its position relative to other internal rotating members, with the result that the segments can perform an extremely stabilized operation.